The present invention is generally related to thermal processing furnaces for processing semiconductor wafers, and particularly to a vertical-type processing furnace including vertical nitride furnaces.
Thermal processing furnaces, also known as diffusion furnaces, have been widely known and used for many years to perform a variety of semiconductor fabrication processes, including annealing, diffusion, oxidation, and chemical vapor deposition (CVD). As a result, these processes are well understood, especially with regard to the impact of process variables on the quality and uniformity of resulting products.
Thermal processing furnaces typically employ either a horizontal-type furnace, or a vertical-tye furnace. For some applications, vertical-type furnaces are preferred because they create less particles during use, thus decreasing the incidence of contamination and wafer waste. In addition, they can be easily automated, and they require less floor space because of their relatively small footprint.
Both conventional types of diffusion furnaces are designed to heat semiconductor wafers to desired temperatures to promote either diffusion of the dopants to a desired depth while maintaining line width smaller than 1 micron, as known, or to perform other conventional processing techniques such as the application of an oxide layer to the wafer or deposition of a chemical vapor layer to the wafer. The heating requirements of the wafer during processing are known and well understood, and thus are closely monitored.
Conventional vertical-type thermal processing furnaces are designed to support the outer tube and inner tube within the furnace in the vertical position. The inner tube is conventionally referred to as a liner, and typical liners include silicon carbide liners which operate above 500xc2x0 Celsius, such as in the TEL a-303i Vertical Nitride Furnace. Although the silicon carbide liners are designed to operate at temperatures above 500xc2x0 Celsius, the current fixtures provided by manufactures for replacing the silicon carbide liners are designed for use at room temperature. Unfortunately, to achieve room temperature, the entire furnace must be inactivated and cooled, which is an exceptionally expensive process. Every time a furnace is brought offline to room temperature, numerous expensive parts need to be serviced and/or replaced before the vertical furnace can be heated again and brought back online. For instance, the inner thermalcouple (TC) needs to be replaced as it is usually contaminated with a nitride film which degrades operational properties and necessitates requalification. This part alone may cost $7,000.00, excluding labor. In addition, a stainless steel manifold and O ring needs to be replaced, which is usually contaminated with ammonia chloride. A fair estimate for bringing a vertical furnace offline and then again back online, such as to replace the silicon carbide liner may cost in excess of $30,000.00
A silicon carbide liner will eventually generate particles in excess of a maximum allowable particle count after a predetermined time, such as a thickness of 3.5 microns, and needs to be replaced. However, the entire furnace does not need to be retrofitted as often, but is conventionally brought offline to provide for the replacement of the silicon carbide liner since the removal fixtures are only designed by the manufacture to operate at room temperature.
Accordingly, there is a need to provide for the retrofitting of a silicon carbide liner within an operating heated vertical furnace, including the installation and removal of the liner from the operating heated semiconductor vertical furnace without causing damage to either the old or new liner, or the furnace itself. Such a solution would significantly reduce the overall operating cost of the vertical furnace by allowing the retrofitting of the silicon carbide liner itself without bringing the furnace offline.
The present invention achieves technical advantages as an liner exchange fixture having a low-friction member and method of operation adapted to permit the retrofitting of a silicon carbide liner in an operating heated semiconductor vertical furnace. The present invention includes an exchange fixture adapted to operate while heated, such as above 500xc2x0 Celsius, and also at room temperature if desired. The exchange fixture can be maneuvered proximate the operating furnace to unlock the liner and lower the liner therefrom at a controlled descent rate to control the cooling rate of the liner from its normal operating temperature. The fixture is also adapted to insert a new liner into the operating furnace at a controlled rate such that the liner is brought up to an operating temperature at a controlled rate to prevent damage thereto. Thus, the film integrity on the remaining operating furnace parts are maintained.
In one preferred embodiment, the exchange fixture comprises an outer ring, and an inner ring residing within the outer ring and adapted to support the liner when elevated to the operating vertical furnace, and when the liner is removed and inserted from/into the operating vertical furnace. The inner ring includes structure adapted to facilitate rotation of the inner ring between a locked position when the liner is elevated in the operating vertical furnace, and an unlocked position when the liner is to be lowered from the operating vertical furnace. Advantageously, the low-friction member is flanged and interposed between and interfacing the inner ring and the outer ring along 2 surfaces, thus facilitating the ease of rotation of the inner ring within the outer ring when the inner ring is both heated proximate the furnace and when lowered from the operating vertical furnace, including at room temperature. This low-friction member accommodates the expansion and contraction of the inner ring within the outer ring due to the heating and cooling cycles of the inner ring when disposed proximate the furnace or when removing the liner from the operating furnace.
An elevator is adapted to support the outer ring for lowering the liner from the operating furnace, and also for elevating the exchange fixture such that the liner is raised into the operating furnace. The first ring includes at least one handle, and preferably two opposing handles, adapted to facilitate rotation of the inner ring within the outer ring along the low friction member when the liner is positioned in the operating vertical furnace.
Each handle has at least two securing points coupled to the inner ring, wherein each handle is uniquely secured at two securing points separated a predetermined actuate distance from one another. Each handle has a lever point radially separated from the inner ring along an axis extending between the two securing points to form a xe2x80x9cTxe2x80x9d relationship relative to the two securing points.
Advantageously, the elevator is adapted to lower the fixture and the supported old liner from the operating furnace at a rate below a predetermined maximum rate to control the rate of temperature decrease of the liner when removed from the operating vertical furnace. Likewise, the elevator is also adapted to elevate the new liner into the operating vertical furnace at a rate below a predetermined maximum rate to control the rate of temperature increase of the liner when inserted into the operating vertical furnace. This controlled ascent and descent rate prevents damage to the old and new liner as it is cooled or brought up to operating temperature.